01 - Preheat the oven to 375°F (190°C) to ensure even cooking.
02 - In a large mixing bowl, whisk together the eggs and milk until well combined.
03 - Fold in the diced ham, chopped spinach, and shredded cheddar cheese. Season lightly with salt and freshly ground black pepper if desired.
04 - Pour the mixture into a lightly greased 9-inch ovenproof nonstick skillet or baking dish, spreading ingredients evenly.
05 - Place in the oven and bake for 20 to 25 minutes, or until the frittata is set in the center and lightly golden on top.
06 - Allow to cool briefly before slicing into wedges and serving warm.